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Folk who actually use f/4 or faster dobs: what is your favourite eyepiece for max field of view ?
We will assume Paracor is being used, which will turn f/4 into f/4.6. Televue will say to avoid exit pupils of >7mm for newtonians. This means that the 31mm Nagler is just about OK on an f/4 dob. Dogma says that the 26mm Nagler or 21mm Ethos is more suitable, generating a better exit pupil. But at the end of the day the 31mm Nagler will give the widest views, especially since the Ethos has much of the field in peripheral vision. It would seem that the 31mm Nagler is popular with owners of fast dobs, indicating that in practise the exit pupil dogma maybe doesnt matter so much.....

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I love 31mm Nagler in my 12.5 inch F/4.06. I use it with a Paracorr. I recently measured my exit pupil, seems to be just about 7mm... if I can keep my eyes open that is.

Jon

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Folk who actually use f/4 or faster dobs: what is your favourite eyepiece for max field of view ?
We will assume Paracor is being used, which will turn f/4 into f/4.6. Televue will say to avoid exit pupils of >7mm for newtonians. This means that the 31mm Nagler is just about OK on an f/4 dob. Dogma says that the 26mm Nagler or 21mm Ethos is more suitable, generating a better exit pupil. But at the end of the day the 31mm Nagler will give the widest views, especially since the Ethos has much of the field in peripheral vision. It would seem that the 31mm Nagler is popular with owners of fast dobs, indicating that in practise the exit pupil dogma maybe doesnt matter so much.....

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The 21mm Ethos is perfect in my F/3.25 24" with Paracorr 2... but I will confess that sometimes (nervously watching over my shoulder just in case the exit pupil police are checking up) I furtively slide in a 31mm T5. I am a habitual offender I know, but the view is really worth the risk and penalties.

Chris

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The 21mm Ethos is perfect in my F/3.25 24" with Paracorr 2... but I will confess that sometimes (nervously watching over my shoulder just in case the exit pupil police are checking up) I furtively slide in a 31mm T5. I am a habitual offender I know, but the view is really worth the risk and penalties.

Chris

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lol I guess this hits the nail on the head, the 31Nagler is supposed to be non-ideal for a fast scope, but 1st hand experience of what it actually delivers is what matters. What got me thinking was Webster Telescopes - their standard scopes are all f/4 or faster. But look at pictures of their scopes, and read their user instructions etc, when you see something in the focusser, it will be the 31 Nagler.

I guess another logical way forward for me would be 31mm Nagler, 21mm Ethos and to cull my 20 and 26mm Naglers. But these Naglers are really comfortable eyepieces to use, easy to look through for long periods, eye positioning is very easy. Looking through the Ethos perhaps requires more effort, even though the wow factor is obvioulsy greater...

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There is a lot of difference between F/3.25 and F/4 when it comes to the 31mm Nagler. Both pretty much require Paracorr and at F/4, you are at F/4.6 with the Paracorr which makes the 31mm Nagler a reasonable choice. At F/3.25 you are working at F/3.74 and a 8.3 mm exit pupil, not so bad if your eye opens reasonably wide but if it only opens to 5mm, then the 21mm Ethos makes more sense.

You're at F/4 with presumably a Paracorr so the 31mm is fine.

Jon

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Plus, I've found that the larger (and brighter) exit pupil of the 31mm Nagler will let me see faint DSO's like the Horsehead and California Nebulas when the smaller exit pupil of the 21mm Ethos won't.

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Plus, I've found that the larger (and brighter) exit pupil of the 31mm Nagler will let me see faint DSO's like the Horsehead and California Nebulas when the smaller exit pupil of the 21mm Ethos won't.

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Your scope is f/4.3.

Below f/4, for me, I find the opposite to be true. I find that the 21mm Ethos shows objects brighter. The exit pupil of the 31mm is just too big for my eye at f/3.6 or f/3.3, and I can notice the difference in lost light. Also, the Ethos are better near the edge of the field.

Of course a Paracorr 2 is always used, so the real f# is 15% higher. (I'm not a fanatic about dark adaptation, by the way, so I could probably get my pupils more dilated if I tried.)

I still occasionally use the 31mm or 41mm Panoptic for fun, though, to fit really large optics like the Rosette in the field of view. Yes, it's like stopping down the scope, but then again that means you don't have to bring along another smaller scope for wide field views. Besides, the telescope police rarely give tickets for exit pupil violations.

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Obviously lots of variables at play here--focal ratio of the scope, how dark the observing site is, the viewing conditions, how wide the observer's pupils can dilate, and so on. Even with my f/4.3 scope I generally prefer the 21mm Ethos over the 31mm Nagler for widefield, and also find that many objects appear brighter and with more contrast with the 21mm Ethos. But I've also found that on some occasions I could see the Horsehead only with the 31mm Nagler, and not with the 21mm Ethos.

I actually used to enjoy using a 40mm Paragon with my scope before upgrading to a 31mm Nagler. Despite the massive exit pupil of over 9mm without a Paracorr (about the same as a 31mm Nagler in an f/3 system with a Paracorr), large, bright DSO's like the Double Cluster and Andromeda still made for excellent eye candy. I knew I was giving up some photons, but in those situations I found it worthwhile to gain the extra TFOV. The 31mm Nagler is better, of course, due to the smaller exit pupil. I've never gotten a ticket from the exit pupil police at star parties, though more than once I've been let off with a warning.

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